The raw materials that make up almost all classes of structural adhesives including epoxies and polyurethanes are derived from fossil fuels. Fossil fuels are not going to last forever and it’s up to us as a community to find sustainable alternatives before it’s too late. Plants present a renewable source of aromatic hydrocarbons that can be converted into a variety of chemicals so its inferable that these will be a source of adhesive raw materials in the future.
The conversion of crops such as corn and sugar cane into the necessary raw materials is the cheapest and easiest way to produce biobased adhesives. However, with a growing population there’s billions of hungry mouths to feed and the use of food stuff in applications such as these is ethically questionable. Using trees as a renewable resource rather than agriculture may be a more suitable option, but even this is not without complications. Firstly, deforestation is already a huge contributor to climate change and the level of deforestation would only increase if wood was also required for the production of petrochemical alternatives. In addition to climate change, we must consider the effect deforestation has on the prevalence of precious habitats and endangered species.
Of the trees that are already harvested for existing purposes not 100% of the material is currently utilised, there is some waste. Lignin makes up approximately a quarter to a third of the mass of vascular plants. In the paper-making process the paper is delignified as lignin weakens the paper, is coloured and yellows in air. Lignin is an unwanted by-product and almost all the lignin produced from paper making is burnt. Therefore, in lignin there is an abundance of material that can be used as a substitute for petroleum based aromatic chemicals, that would otherwise have been wasted.
For lignin based raw materials to compete commercially with petrochemical based chemicals more research and development is required. The structure of lignin is complex and hence the downstream processing is significant and energy costs are high. However, work is being carried out and the process is becoming steadily more efficient. The cost of producing aromatic fine chemicals is steadily decreasing and the cost of petrochemicals will start to increase due to lack of availability in the not too distant future. It is likely lignin-based bio adhesives will be common place before too long.
The technical team at Structural Adhesives Ltd are researching into biobased raw materials currently on the market and keeping a keen eye on developments in this sector.